1. Field of the Invention
The present invention relates to an apparatus and method for transmitting data by using Multi-round Contention Avoidance (MrCA). More particularly, the present invention relates to an apparatus and method for transmitting data by using MrCA in a wireless network employing a wireless random access channel or a distribution access scheme.
2. Description of the Related Art
Slotted ALOHA is an access scheme generally used in a next generation wireless access environment that uses a random access channel. In the slotted ALOHA scheme, when it is desired to transmit data using a wireless resource, a user attempts to transmit the data in a time slot immediately subsequent to the current time slot. If another user is using the same channel, the two users cannot successfully transmit a frame due to mutual interference, which leads to retransmission. In retransmission, the user waits for a random time to prevent the collision from occurring again, and then transmits the data in a corresponding slot. However, although the slotted ALOHA scheme has been designed aiming at simplicity, it has a significant shortcoming in terms of interference with other users. Specifically, a theoretical throughput of the slotted ALOHA is e−1, or approximately 0.368. This means that, in practice, only about 37% of an entire channel is used in practical transmission under optimal conditions.
With a throughput of only 37%, it is not possible to provide services for a system such as a wireless Local Area Network (LAN) in which a random access scheme is generally used in data transmission. Therefore, the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard has proposed the use of a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme. In the CSMA/CA scheme, before a user attempts to transmit data through a wireless channel, the user first determines if another user is using the channel, and, in order to minimize collisions, waits for a random time before attempting to transmit the data even if no user is using the channel. In other words, in the CSMA/CA scheme, when the user has a frame to be transmitted, the user first determines a state of a wireless channel to be used, and, if a signal of another user is sensed, waits until the wireless channel is idle, and otherwise, immediately proceeds to a collision avoidance process. In the collision avoidance process, a random time is allocated, and then the user waits for that time before attempting to transmit data. The CSMA/CA scheme prevents data from being concurrently transmitted by several users through a non-busy channel, thereby reducing a collision probability. However, since the CSMA/CA scheme uses the wireless resource in a very cautious manner as compared to the slotted ALOHA scheme, the wireless resource is less effectively used in practice. In addition, there is a problem in that, even with a small number of users, time is not efficiently allocated, and with a large number of users, collision probability and performance deterioration are both increased. In particular, a collision avoidance function of the CSMA/CA scheme may cause an unequal distribution of resources, and thus a large amount of resources may be exclusively used by some users.